Blend flour, soda, salt, and cream of tartar in a large bowl. Cut in butter until mixture resembles cornmeal. (You may do this with a pastry knife or food processor; I prefer the latter just because it is faster, although I then need to wash another bowl.)

Divide dough in half, and shape each half into fairly smooth rounds approximately ¾-inch think. Be careful not to overwork the dough or it will become tough. Cut each circle into 8 wedges.
Place on a parchment-lined baking sheet.